John Mannering (aka 'The Baron') is a retired cracksman and jewel thief who now runs an antique shop, 'Quinns', in London's Mayfair. He decides to open a branch in Boston and at the same time move to an Elizabethan Manor House known as Harden Court. However, the present owner of the house disappears, and a man is found dead in one of its secret stairways. Further mystery ensues and then 'The Baron' suffers a devastating blow before he can open his new branch, and before he can get to grips with determining what is going on – he is arrested for murder.